Fluctuations In River Discharge Research Articles

Dynamic Analysis of Changes in Jambu Riverbed and Banks: Case Study Around Cikuya Bridge

Several cross-sections of the Jambu River, particularly around the Cikuya Bridge, have experienced bank collapse phenomena. This paper interprets the issues related to bank collapse and its impact on the flow capacity of the Jambu River, especially around the Cikuya Bridge. Morphological changes were simulated using a sediment transport model implemented in the Hydrologic Engineering Center's River Analysis System (HEC-RAS) 6.3.1, integrated with the ARS-USDA Bank Stability and Toe Erosion Model (BSTEM). The simulation results indicate that over a period of 10 years, the thalweg elevation (the lowest point of a riverbed) of the Jambu River around the Cikuya Bridge is predicted to experience deposition in 17 cross-sections and erosion in 15 cross-sections. The highest deposition occurs at the cross-section below the Cikuya Bridge, with a thalweg elevation change of 0.59 m. This warrants attention as the storage capacity of the cross-section decreases by 7% from the initial condition. Predictions indicate that bank collapse will occur in 7 cross-sections over the next 10 years. This is attributed to the steep slopes of silt and clay banks, exceeding 45 degrees, and the reduced safety factor of bank stability due to groundwater pressure influenced by river discharge fluctuations and tidal effects reaching the Jambu River. Bank collapse impacts the elevation change of the riverbed and adds load to the sediment transport model from the collapsing cross-sections to the downstream sections. Keywords: Jambu River, Cikuya Bridge, Cilacap, sediment transport, bank stability and toe erosion model

Impacts of Quaternary climatic changes on the diversification of riverine cichlids in the lower Congo River.

Climatic and geomorphological changes during the Quaternary period impacted global patterns of speciation and diversification across a wide range of taxa, but few studies have examined these effects on African riverine fishes. The lower Congo River is an excellent natural laboratory for understanding complex speciation and population diversification processes as it is hydrologically extremely dynamic and recognized as a continental hotspot of diversity harboring many narrowly endemic species. A previous study using genome-wide SNP data highlighted the importance of dynamic hydrological regimes to the diversification and speciation in lower Congo River cichlids. However, historical climate and hydrological changes (e.g., reduced river discharge during extended dry periods) have likely also influenced ichthyofaunal diversification processes in this system. The lower Congo River offers a unique opportunity to study climate-driven changes in river discharge, given the massive volume of water from the entire Congo basin flowing through this short stretch of the river. Here, we, for the first time, investigate the impacts of paleoclimatic factors on ichthyofaunal diversification in this system by inferring divergence times and modeling patterns of gene flow in four endemic lamprologine cichlids, including the blind cichlid, Lamprologus lethops. Our results suggest that Quaternary climate changes associated with river discharge fluctuations may have impacted the diversification of species along the system. Our study, using reduced representation sequencing (2RADseq), indicates that the lower Congo River lamprologines emerged during the Early-Middle Pleistocene transition, characterized as one of the earth's major climatic transformation periods. Modeling results suggest that gene flow across populations and between species was not constant but occurred in temporally constrained pulses. We show that these results correlate with glacial-interglacial fluctuations. The current hyper-diverse fish assemblages of the lower Congo River riverscape likely reflect the synergistic effects of multiple drivers fueling complex evolutionary processes through time.

Analysing the performance of the NARX model for forecasting the water level in the Chikugo River estuary, Japan

Estuaries are dynamic environments which are driven by various natural processes like river discharge, tides, waves, influx of saline water and sediments, etc. These ecosystems are the most sensitive to sea level rise and fluctuations in river discharge associated with climate change. A direct response of sea level rise and river discharge can be observed in the water level of estuaries. However, existing models have not considered these parameters for forecasting water level. This paper focuses on developing a water level forecast model for the Chikugo River estuary in Japan using Nonlinear Autoregressive with Exogenous inputs (NARX Model). NARX neural network was used to do the one-step-ahead prediction of water level considering the various parameters that can very well be influenced by climate change: previous water level, river discharge, and salinity. Accordingly, three models were developed: (i) Model I considering previous water level; (ii) Model II additionally considering river discharge; and (iii) Model III additionally considering salinity. All the models showed appreciable performance in forecasting the water level. Model III had the best correlation with the water level with a cross-correlation value of 0.6030, while the river discharge had only a cross-correlation of 0.1113 indicating that the Chikugo River estuary is tide-dominated. The model was trained using different combinations of available data - previous water level, river discharge, and salinity. Cross-correlation results showed a better correlation between water level and salinity than various other combinations trained. Therefore, tidal intrusion influences the water level in the estuary, thereby depicting that sea level rise can affect the water level, and its influence can be well predicted by the developed model. The water level significantly affects the flora and fauna and the predictability of future estuarine floods can help in taking necessary mitigation strategies.

Hydro-Climatic and Vegetation Dynamics Spatial-Temporal Changes in the Great Lakes Depression Region of Mongolia

The Great Lakes Depression region basin is among the most sensitive regions to vegetation change due to climate change. This study estimated spatial-temporal changes and relationships in hydro-climate and vegetation dynamics in the basin. Studying the spatial-temporal variation between vegetation dynamics and hydro-climate in this basin is essential for assessing climate change and sustainability. This research involved an examination of the mean yearly air temperature, overall annual rainfall, fluctuations in river discharge, vegetation cover, and alterations in vegetation types within the selected basin stations. This was accomplished through the utilization of hydro-meteorological analysis, satellite assessment, land cover determination, and statistical analysis. Over the course of the study, it was observed that the average annual air temperature increased at all stations (with a positive change of Z = +1.16). The amount of precipitation decreased (Z = −0.79), especially from 2000 to 2014, and its statistical significance decreased. During the study period, average river discharge significantly decreased (Z = −3.51). Due to these combined factors, the lake’s water level also decreased (Z = −2.03). Vegetation cover change varied in high mountains, near river and lake water surfaces, and in arid regions. Changes in air temperature and precipitation in the current year determine vegetation cover. Because of the large amount of precipitation in the summer months from 2000 to 2010 and 2020, the growth of vegetation cover during that period was relatively good. This study was conducted in arid and semi-arid regions of Central Asia and demonstrates the impact of climate change on changes in vegetation cover.

Large-scale seasonal forecasts of river discharge by coupling local and global datasets with a stacked neural network: Case for the Loire River system

Accurate prediction of river discharge is critical for a wide range of sectors, from human activities to environmental hazard management, especially in the face of increasing demand for water resources and climate change. To address this need, a multivariate model that incorporates both local and global data sources, including river and piezometer gauges, sea level, and climate parameters. By employing phase shift analysis, the model optimizes correlations between the target discharge and 12 parameters related to hydrologic and climatic systems, all sampled daily. In addition, a stacked LSTM - a more complex neural network architecture - is used to improve information extraction ability.Exploring river dynamics in the Loire-Bretagne basin and its surroundings, the investigation delves into predictions in daily time steps for one, three, and six months ahead. The resulting forecast features high accuracy and efficiency in predicting river discharge fluctuations, showcasing superior performance in forecasting drought periods over flood peaks. A detailed examination on data used highlights the significance of both local and global datasets in predicting river discharge, where the former dictates short-term predictions, while the latter drives long-range forecasts. Seasonally extended forecasting confirms a strong connection between the forecast leading time and the shift in data correlation, with lower correlation at a lag of 3 months due to seasonal changes affecting forecast quality, compensated by a higher correlation at a longer lag of 6 months. Such mutual effect in this multi-time-step forecasting improves the predictive quality of a six-month horizon, thus encourages progress in long-term prediction to a seasonal scale. The research establishes a practical foundation for effectively utilizing big data to leverage long-term forecasting of environmental dynamics.

The morphology of fluvial‐tidal dunes: Lower Columbia River, Oregon/Washington, USA

AbstractThis article quantifies changes in primary dune morphology of the mesotidal Lower Columbia River (LCR), USA, through ~90 river kilometres of its fluvial‐tidal transition at low‐river stage. Measurements were derived from a multibeam echo sounder dataset that captured bedform dimensions within the thalweg (≥ 9 m depth; ≥ 0.7) of the LCR main channel. Measurements revealed two categories of dunes: (i) fine to medium sand ‘fluvial‐tidal to tidal’ (upstream‐oriented, simple, and two‐dimensional) low‐angle dunes (heights ≈ 0.3–0.8 m; wavelengths ≈ 10–25 m; mean lee‐angles ≈ 7°–11°), and (ii) medium to coarse sand ‘fluvial’ (downstream‐oriented, compound, and 2.5‐dimensional to three‐dimensional) low‐angle dunes (heights ≈ 1.5–3 m; wavelengths ≈ 60–110 m; mean lee‐angles ≈ 11°–18°). At low‐river stage, where ≥ 0.7, approximately 86% of the fluvial‐tidal transition is populated by ‘fluvial’ dunes, whilst ~ 14% possesses ‘fluvial‐tidal to tidal’ dunes that form in the downstream‐most reaches. Thus, throughout the majority of the deepest channel segments of the fluvial‐tidal transition, seaward‐oriented river and ebb‐tidal currents govern dune morphology, whilst strong bidirectional tidal‐current influence is restricted to the downstream most reaches of the transition zone. Two mechanisms are reasoned to explain dune low‐angle character: (1) high‐suspended sediment transport near peak tidal‐currents that lowers the leeside‐angles of ‘fluvial‐tidal to tidal’ dunes, and (2) superimposed bedforms that erode the crests, leesides, and stoss‐sides, of ‘fluvial’ dunes, which results in the reduction of leeside‐angles. Fluctuations in river discharge create a ‘dynamic morphology reach’ at depths where ≥ 0.7, which spans river kilometres 12–40 and displays the greatest variation in dune morphology. Similar channel reaches likely exist in fluvial‐tidal transitions with analogous physical characteristics as the LCR and may provide a distinct signature for the fluvial‐tidal transition zone.

Grass carp larval density synchronised with river discharge fluctuations in the subtropical Pearl River, China

AbstractRiver discharge/flow exerts fundamental driving effects on the river ecosystem and larval abundance dynamics. In the subtropical Pearl River, China, the species‐specific effects of river discharge on the occurrence of grass carp larvae remain unknown. We performed cross wavelet analysis, using data on the daily density of larvae collected from 2006 to 2013 at a fixed site downstream in the Pearl River, to explore the temporal correlation between river discharge/water temperature and larval density. We further used the conditional random forest and generalised additive models to determine relevant environmental effects on their relationship. Grass carp larvae appeared from late April to early October, but mainly during June and July. River discharge, but not water temperature, showed significant coherence and in‐phase relationship with larval density. For discharge in significant coherence with larval density, it ranged from 4,740 to 28,700 m3/s, with peak discharge from 4,900 to 30,900 m3/s, and the discharge fluctuation state from −16 to 10 days (where − indicates the falling stage and + the rising stage). Maximum daily temperature/water temperature, ammonia‐nitrogen concentration, peak discharge and discharge contributed the most to the variations in coherence and phase relationships between discharge and larval densities over the short timescale (<32 days) and accounted for 22.4% of coherence variation, 19.7% of in‐phase degrees and 15% of variation in phase lagging. These suggest that a combination of ecological regulation and water environment control would be efficient to promote the recruitment of grass carp and relevant freshwater fish species.

Climate variability effects on eutrophication of groundwater, lakes, rivers, and coastal waters in the Netherlands

Many aquatic ecosystems in densely populated delta areas worldwide are under stress from overexploitation and pollution. Global population growth will lead to further increasing pressures in the coming decades, while climate change may amplify the consequences for chemical and ecological water quality. In this study, we explored the effects of climatic variability on eutrophication of groundwater, streams, rivers, lakes, estuaries, and marine waters in the Netherlands. We exploited the relatively dense monitoring information from the Dutch part of the Rhine-Meuse delta to evaluate the water quality response on climatic variability, in combination with anthropogenic pressures.Our results show that water quality of all water systems in the Netherlands is affected by climate variability in several ways: 1) through the process of global climate change (mainly temperature and sea level rise), 2) through changes Atlantic ocean circulation patterns (more southwestern winds), 3) through changes in continental precipitation and river discharge fluctuations, and 4) through local climatic fluctuations. The impact of climate variability propagates through the hydrological system ‘from catchment to coast’. The fluctuations in water quality induced by climatic variability shown in this study give a preview for the potential effects of climate change.

Conservation of Jatigede Reservoir catchment area based on sediment and water yield control

Jatigede Reservoir serves to control floods in Indramayu area. The reservoir irrigate rice fields by 90,000 ha, supply raw water for clean water by approximately 3,500 l/sec, and produce electricity by 110 MW. Yet, the condition of the Cimanuk watershed is reported in a critical situation. It was characterized by high soil erosion and high fluctuations in river discharge. This study aims to evaluate the sedimentation and river flows that entering the Jatigede Reservoir. The rainfall-runoff simulation determined by SWAT (Soil and Water Assessment Tools) on Jatigede Reservoir is based on existing land use. According to SWAT, it showed the possibility of current land use on annual crop and garden land which is carried out some conservative measurements, such as terrace, grass strip, and ditch and also building area that constructed an infiltration well would reduce the sediment yield from around 9.05 to 5.96 million tons per year. Not only that, but also runoff will decline from 99.7 to 75.8 mm per year. If the measurements are based on land use according to the 2011-2030 Spatial Plans of Garut Regency and Sumedang Regency, the sediment yield can be reduced to 4.97 million tons per year and runoff which become 97.6 mm per year. However, if the environmental degradation of the Cimanuk watershed is allowed to continuously increase that is marked by changes in uncontrolled land use, it will raise the sediment yield and runoff by about twice as the current conditions, so that it can threaten the sustainability of the function of Jatigede Reservoir.

Estuary-shelf interactions off the Changjiang Delta during a dry-wet seasonal transition

Estuary-shelf interaction is very complex and vital for maintaining healthy ecosystem in the estuaries and adjacent seas. The topic has been intensively studied through cruise observations and numerical models, but less by long-term observations at a fixed station. We present here for the first time roughly 2-months ADCP and CTD continuous data from the Xiaoqushan pilot station of seafloor observatory, aiming to deliberate river plume frontal processes off the Changjiang Estuary in response to river discharge transition from the dry to wet season in 2009. Multiple lines of evidence attest that inner river plume is always in a bottom-trapped form, but isohalines and isothermals are very sensitive to seasonal variations in freshwater input, wind climate and surface heating. Semidiurnal oscillations of salinity and temperature are good tracers for seasonal variations in plume frontal processes. In the dry season, both salinity and temperature have weak semidiurnal oscillations due to minimal cross-shore straining under strong mixing conditions near the inner plume front where isohaline and isothermal are nearly vertical with small horizontal salinity and temperature gradient. They are suddenly interrupted by a sharp increase of semidiurnal salinity oscillations owing to the arrival of newly established plume front with a less steep isocline slope but a maximum horizontal salinity gradient of 0.8 psu/km. The response time of inner plume front to the first discharge increasing pulse is roughly two weeks, but should change a lot when examined at different plume locations and under varied river-discharge increasing magnitudes and rates. The frontal processes mirror well the river discharge fluctuations in the transitional period which lasts for a few weeks before entering a typical wet season. The latter features strongest semidiurnal temperature oscillations linked with summer surface heating, and highly depressed semidiurnal salinity oscillations because the main plume path shifts from southward to northeastward due to alternating southerly to northerly prevailing winds. The three stages of inner plume frontal processes can be more clearly demarcated by the wavelet power spectral and the amplitudes of semidiurnal/diurnal oscillations of salinity and temperature through wavelet transform and the associated band-pass filtering methods. The seasonal plume frontal transition has been vividly portrayed for the first time through secular observation at the fixed station in the river plume region, significantly improving our understanding their controlling factors and mechanisms.

Spatio-statistical analysis of rainfall fluctuation, anomaly and trend in the Hindu Kush region using ARIMA approach

This paper focuses on the spatio-statistical analysis of rainfall fluctuation, anomaly and trend in the Hindu Kush region using auto-regressive integrated moving averages (ARIMA) approach. In the study area, trend in rainfall has significant impact on fluctuations in river discharge, which ultimately led to floods and hydrological drought. In this study, rainfall has been used as a climatic parameter. For this study, average annual and mean monthly rainfall data for Dir, Timergara, Saidu, Chitral, Drosh, Malam Jabba and Kalam meteorological stations located in the study region were gathered from Regional Meteorological Center Peshawar. In the study area, the rainfall is mostly received during two prominent periods, i.e., summer rainfall from monsoon, whereas winter and spring rainfall from western depressions. In the study area, Malam Jabba has recorded the heavy mean annual rainfall (1647 mm) and is considered as the humid station followed by met station Dir with a 1362 mm mean annual rainfall. Similarly, Saidu met station received 1050 mm mean annual rainfall and Kalam 1038 mm, whereas Timergara, Drosh and Chitral recorded 796 mm, 568 mm and 458 mm, respectively. The temporal data regarding rainfall were calculated and simulated in Addinsoft Excel state 2014 by applying ARIMA statistical model for trend prediction, fluctuations and anomaly. The analysis indicates that in terms of rainfall, an increasing trend has been detected at Dir, Chitral, Saidu and Kalam meteorological stations, whereas a declining trend has been recorded at Timergara, Drosh and Malam Jabba meteorological stations. In terms of rainfall anomaly, the met station Dir has indicated comparatively high positive anomaly. Contrary to this, the met stations of Saidu and Drosh have experienced negative rainfall anomaly.

Land Use Potential on Water Balance Based on SWAT Method in Saddang Watershed in Bendung Benteng Irrigation System

Saddang Watershed (DAS) as a large watershed in Sulawesi, rich in natural resource potential in the form of land, topography, slope, geology, soil, vegetation, climatology; rainfall, temperature, humidity, and sunshine. In maintaining and utilizing (watershed management) availability and water requirements for; humans, plants and animals. The availability and demand of water in watershed management requires the role of land in regulating agroclimatology and hydrology conditions. The water balance approach method used is SWAT (Soil and Water Assessment Tool) method of soil and water assessment tools, to determine the condition of availability and demand of water in an effort to maintain water flow conditions at all times (number and distribution) of Bendung Benteng irrigation system, which is capable of supply water for paddy field irrigation in two regencies of South Sulawesi’s paddy granaries namely Pinrang Regency and Sidrap Regency. According to the Schmidth-Fergusson climate classification, the type of climate in Saddang watershed area belongs to type C climate = slightly wet area with tropical rainforest vegetation, the average amount of rainfall ranges from 2.155 mm/year. This indicates that there is large level of rainfall every year and land use with a forest area of 676,39 or 26,41% of the watershed area, thus Saddang watershed is able to save tremendous amount of water supply. Based on the results of the water balance analysis using SWAT method, the amount of water available in the average watershed ; 3.133 mm year-1, the amount of water being flowed ; 1.040,9 mm, and stored as ground water ; 29,60 mm, as well as direct runoff ; 366,9 mm and flow coefficient of 0,45. Hence, there is 45% of the flow loss as surface stream and there is 55% of the flow stored in the watershed, and the model application is categorized as good both in conducting simulations and validating the flow discharge on Saddang River. Watershed processing classified as having good watershed conditions, because one indicator of a watershed's water performance can be seen from the river discharge fluctuation. River discharge fluctuations can be seen from the river regression coefficient (KRS), which is a number that shows ratio between maximum discharge (Qmax) and minimum discharge (Qmin). The highest discharge (Qmax) was 30.805 m³/sec while the lowest discharge (Qmin) was 994 m³/sec. The regression coefficient value (KRS) of Saddang River watershed was 26.650 m³/sec. Based on the results of the 2017 data analysis, the condition of Saddang watershed provides surplus value of 1.911.986 (m3 year-1), out of the total water availability of 2.155.273 (m3 year-1) minus the total irrigation water requirement of 243.286,50 m3 year-1, with the pattern of planting paddy-paddy-secondary crops (palawija). Therefore, Saddang watershed has the ability to store large amounts of water throughout the year

Evaluating snow cover changing trends of the Western Indian Himalaya

The extent of snow cover in the Western Indian Himalaya determines the fluctuations in river discharge during the summer months and affects the water supply for hydroelectric generation, agriculture and related socio-economic systems which further affect the livelihood of the population in the area and downstream. Despite this importance, there is a lack of information about this region primarily due to the complexities of the processes involved in snow hydrology and the lack of snow cover and depth data in the high elevation areas. Periodical monitoring of the snow cover area (SCA) is an indispensable demand for short-term forecasts of the daily river flows and seasonal forecasts of run-off volume. Therefore, this study is an attempt to assess the annual, seasonal and monthly variations in the extent of snow cover of the Western Indian Himalaya. SCA was estimated using the MODIS/Terra Snow Cover 8-Day L3 Global 500 m (MOD10A2) data for the period 2000–2015. Monthly composite maps of SCA were prepared from 8 days composite snow cover area maps for the Kashmir, Himachal and Kumaon Himalaya. The study found a reduction in snow cover in the Indian Western Himalaya. The inter-seasonal variation in SCA was also observed in the study area. The study found an inter-regional variations in the extent of snow cover in the Western Indian Himalaya during the period of analysis. Emerging changes in the extent of snow cover would influence the availability of water in the near future.

Scaling characteristics of mountainous river flow fluctuations determined using a shallow-water acoustic tomography system

The aim of this study is to investigate the scaling exponent properties of mountainous river flow fluctuations by detrended fluctuation analysis (DFA). Streamflow data were collected continuously using Fluvial Acoustic Tomography System (FATS), which is a novel system for measuring continuous streamflow at high-frequency scales. The results revealed that river discharge fluctuations have two scaling regimes and scaling break. In contrast to the Ranting Curve method (RC), the small-scale exponent detected by the FATS is estimated to be 1.02 ± 0.42% less than that estimated by RC. More importantly, the crossover times evaluated from the FATS delayed approximately by 42 ± 21 hr ≈2–3 days than their counterparts estimated by RC. The power spectral density analysis assists our findings. We found that scaling characteristics information evaluated for a river using flux data obtained by RC approach might not be accurately detected, because this classical method assumes that flow in river is steady and depends on constructing a relationship between discharge and water level, while the discharge obtained by the FATS decomposes velocity and depth into two ratings according to the continuity equation. Generally, this work highlights the performance of FATS as a powerful and effective approach for continuous streamflow measurements at high-frequency levels.

Hydrology Simulation of Ukud River in Lati Coal Mine

Development of mine pit and overburden disposal has caused dynamic changes in the catchment area of Ukud River, one of the rivers that flow through Lati Mining Operation. The maximum discharge of the river reached 13m3/second and the catchment area occupied a total area of 1901.7 hectares. Since the mining operations started, the river discharge fluctuations have changed considerably. In addition, the catchment area that was dominated by overburden disposal area contained sulphide minerals that potentially degrade the water quality of Ukud River due to the formation of acid mine drainage. Hydrological studies are essential to investigate potential environmental impacts of the mining activities. This study was conducted to determine the characteristics of the hydrologic systems in the mining area using semi-distributed models that can be used to simulate the river flow within catchment area.

Discriminant analysis for characterization of hydrochemistry of two mountain river basins of contrasting climates in the southern Western Ghats, India.

Discriminant analysis (DA) was performed on river hydrochemistry data for three seasons (i.e., monsoon (MON), post-monsoon (POM), and pre-monsoon (PRM)) to examine the spatio-temporal hydrochemical variability of two mountain river basins (Muthirapuzha River Basin (MRB) and Pambar River Basin (PRB)) of the southern Western Ghats, India. Although the river basins drain tropical mountainous terrain, climate and degree of anthropogenic disturbances show significant differences (i.e., humid, more disturbed MRB vs semiarid, less disturbed PRB). In MRB, TDS, Na(+), pH, Mg(2+), and K(+) are the attributes responsible for significant hydrochemical variations between the seasons, while Cl(-), TH, and Na(+) are the predictors in PRB. The temporal discriminant models imply the importance of rainfall pattern, relative contribution of groundwater toward stream discharge and farming activities in hydrochemistry between the seasons. Inclusion of hydrochemical attributes (in the temporal discriminant functions) that can be derived from both natural and anthropogenic sources suggests that ionic enrichment strongly depends on the seasons, and is mainly due to the variability in the intensity of anthropogenic activities as well as fluctuations in river discharge. In spatial discriminant models, Cl(-) is the only variable responsible for hydrochemical variations between the basins (during MON), whereas Si discriminates during POM and PRM, implying the role of atmospheric supply, anthropogenic modifications as well as intensity of weathering. In the spatial discrimination models, misclassification of hydrochemistry data between MRB and PRB can be attributed to the overlapping effect of humid climate of MRB extending toward the upstream of (semiarid) PRB. This study underscores the versatility of DA in deciphering the significance of climatic controls on hydrochemical composition of tropical mountain rivers.

Environmental flow assessments in estuaries based on an integrated multi-objective method

Abstract. An integrated multi-objective method for environmental flow assessments was developed that considered variability of potential habitats as a critical factor in determining how ecosystems respond to hydrological alterations. Responses of habitat area, and the magnitude of those responses as influenced by salinity and water depth, were established and assessed according to fluctuations in river discharge and tidal currents. The requirements of typical migratory species during pivotal life-stage seasons (e.g., reproduction and juvenile growth) and natural flow variations were integrated into the flow-needs assessment. Critical environmental flows for a typical species were defined based on two primary objectives: (1) high level of habitat area and (2) low variability of habitat area. After integrating the water requirements for various species with the maximum acceptable discharge boundary, appropriate temporal limits of environmental flows for ecosystems were recommended. The method was applied in the Yellow River estuary in eastern Shandong province, China. Our results show that, while recommended environmental flows established with variability of potential habitats in mind may not necessarily benefit short-term survival of a typical resident organism on a limited temporal or spatial scale, they may encourage long-term, stable biodiversity and ecosystem health. Thus, short-term ecosystem losses may be compensated by significant long-term gains.

Natural born indicators: Great cormorant Phalacrocorax carbo (Aves: Phalacrocoracidae) as monitors of river discharge influence on estuarine ichthyofauna

The ecological traits of piscivorous marine birds have been acknowledged to reflect ecosystem changes. We used the great cormorant as our indicator species in the Minho estuary (NW-Iberian Peninsula, Europe) to assess the temporal variation of their diet and the factors that could influence that variation. Pellets were collected in a night roost, located centrally in the estuary, during two consecutive wintering periods (2005–2006 and 2006–2007). The great cormorant population showed a high degree of feeding plasticity and most of the variation in cormorants' diet was attributed to river discharge fluctuations. Overall, during periods of increased river discharge, marine and marine opportunistic species disappeared from diet, whereas freshwater species increased. The cormorants in this study were using a roost in the middle of the estuary, so they were facing a changing food base over time, in accordance to variation in river discharges. The birds did not keep their diet constant but rather took what became locally available, notwithstanding their broad foraging range. Therefore, we suggest that great cormorants may be considered good samplers of local ichthyofauna and thus, temporal variation in the local prey can be followed by analyzing cormorants' diet.

Wavelet analysis of the annual discharge records of the world’s largest rivers

The determination of the temporal variability of water resources is of high importance with respect to long-term water policy. This contribution provides a wavelet-based global analysis of 55 large river discharge fluctuations located on the five continents. It shows that large river runoff records should be considered as valuable climatic proxies (such as temperature or precipitation records) since discharge series integrate intermittent 4-year and longer processes. Effectively, continuous Morlet wavelet analysis allows to identify statistically significant bands of intermittent fluctuations from interannual 5–8-year to decadal, 12–15-year, bidecadal, 28-year fluctuations and 4–70-year considering the longest time series available in Europe and North America. Reasonable physical relationships between land–water cycle oscillations and climate forcings (such as ENSO or NAO) are documented and investigated but all these results should later on be more systematically confirmed by cross-wavelet analyses.

Quantifying urbanization-associated changes in terrestrial hydrologic system memory

A common feature of watershed urbanization is increased hydrograph ‘flashiness,’ whereby river discharge fluctuations grow more erratic. Such changes might be intuitively interpreted as a decrease in watershed-scale hydrologic system memory. Here, I investigate this hypothesis through a paired-catchment experiment. The serial correlation coefficient, a common metric of short-term time series memory, is applied to daily winter streamflow data from urbanizing and rural watersheds in the Puget Sound lowland of Washington State, USA. Statistical comparisons confirm that this metric shows highly significant decreases over time in the catchment undergoing land use change, but not in the control watershed, which remains rural over the hydrometric record. Moreover, the mean serial correlation coefficients are statistically indistinguishable between the two catchments over the early period of record, when both watersheds are largely rural, whereas the system memory is far weaker in the urbanized stream relative to the rural stream over the late period, following land use change in the former. The results appear readily interpretable in terms of the physical hydrologic changes typically associated with urbanization. The serial correlation coefficient thus appears to be an instructive measure of urbanization impacts for small streams in this region.